This invention relates to curable blends of previously-vulcanized fluoroelastomers with fluorine-free elastomers.
Fluoroelastomers are relatively expensive specialty polymers which exhibit excellent heat stability and fluid resistance. Conventional techniques used to transform uncured compounded elastomers, including fluoroelastomers, into cured fabricated parts such as o-rings, seal elements, and gaskets generate significant quantities of vulcanized elastomer waste, e.g. as flash, transfer pads, and runners from molding operations. Such material is not scrap in the sense of defective parts, but it does represent waste and its formation results in an economic penalty inevitably associated with manufacture of elastomer parts. With respect to fluoroelastomers, the economic penalty is magnified because of the high cost of such polymers. An inexpensive method for re-use or recycle of vulcanized fluoroelastomer waste would consequently permit a more effective utilization of material and energy in the production of fluoroelastomer manufactured goods. However, attempts to develop such processes have met with only limited success. For example, an obvious recycle process would involve blending a portion of the vulcanized fluoroelastomer with uncured fluoroelastomer and using the blend composition to produce molded goods. Use of significant proportions of vulcanized fluoroelastomer waste as an additive, however, results in sacrifice of processability and physical properties.
The high cost of fluoroelastomers makes the use of these materials prohibitive in many applications. Consequently, attempts to provide less expensive compositions having performance characteristics which approach those of fluoroelastomers have been made. For example, blends of fluoroelastomers with hydrocarbon elastomers are known, but the properties of such compositions are generally not acceptable because the two classes of elastomers are essentially incompatible. In addition, processes have been disclosed wherein mixtures of fluoroelastomer and hydrocarbon polymer components are dynamically cured. For example, Sakai et al, in U.S. Pat. No. 5,206,293, disclose rubber compositions obtained by subjecting mixtures of fluoroelastomer, polyethylene or an ethylene copolymer, and organic peroxide to shearing deformation at elevated temperature. This procedure provides a composition wherein the ethylenic resin is crosslinked, but the fluoroelastomer is uncrosslinked. Tabb, in copending U.S. patent application Ser. No. 08/143,262, now U.S. Pat. No. 5,412,034 discloses co-curable blends of fluoroelastomer and elastomeric ethylene copolymer, in which both blend components are simultaneously cured by the same curing agent.
It would not be expected that blends of vulcanized fluoroelastomer with hydrocarbon elastomers would provide useful compositions because of the above-described incompatibility of these polymers and the deleterious effect on physical properties which results when previously vulcanized fluoroelastomer is blended with uncured, virgin fluoroelastomer. However, it has now been found that vulcanized fluoroelastomer can be blended with non-fluorinated elastomers to produce elastomers having excellent physical properties.